In a vehicle, the powertrain or powertrain system refers to the components that provide the power to propel the vehicle. These components include the engine, transmission, the drive/propeller shaft, differentials, and a final drive. In operation and for an internal combustion engine, the engine combusts a fuel to generate mechanical power in the form of a rotating crankshaft. The transmission receives the rotating crankshaft and manipulates the engine speed (i.e., the rotation of the crankshaft) to control a rotation speed of the drive/propeller shaft, which is also coupled to the transmission. The rotating drive shaft is received by a differential, which transmits the rotational power to a final drive (e.g., wheels) to effect a movement of the vehicle. In an automobile, the differential enables the wheels, on a shared axle, to rotate at different speeds (e.g., during a turn, the outer wheel spins faster relative to the inner wheel to allow the vehicle to maintain its speed and line of travel).
In regard to a hybrid vehicle, conventional hybrid engine systems generally include both an electric motor and an internal combustion engine that are capable of powering the drivetrain in order to propel the car. A hybrid vehicle can have various configurations. For example, in a parallel configuration both the electric motor and the internal combustion engine are operably connected to the drivetrain/transmission to propel the vehicle. In a series configuration, the electric motor is operably connected to the drivetrain/transmission and the internal combustion engine indirectly power the drivetrain/transmission by powering the electric motor.
During travel of a vehicle, there are many instances when the vehicle may stop before the destination is reached. This may occur, for example, when the vehicle stops at traffic lights, cross-walks, stop signs and the like. A vehicle with an electrified powertrain may enable a stop/start function for starting and stopping the vehicle engine during a driving event. For example, the engine is shut down if no power is required (e.g., while waiting at a traffic light). A battery of the vehicle may satisfy the vehicle's entire electrical needs when the engine is off. As soon as power is requested (e.g., when the driver releases the brake pedal), the engine is automatically restarted. By avoiding unnecessary engine idling, the vehicle's fuel economy may be improved. For this reason, it is desirable to use the engine stop/start function as much as possible when certain engine stop conditions are satisfied.
For a vehicle that is temporarily stopped on a hill, the engine or motor must work to maintain just enough torque to hold the vehicle from rolling backwards. This is known as a “hill hold.” When operating under this condition, the motor will use energy stored in the battery. If the engine is shut down, the battery will alone provide the torque needed and the battery life will be negatively affected. In addition, there are other situations where the engine is desired to work during a temporary stop of the vehicle, for example, in the situation of power steering or when heating, ventilating, and air conditioning (HVAC) is on. Further, in many stop-and-go situations or vehicle creep situations (e.g., as commonly experienced during heavy traffic), vehicles do not remain stopped long enough to effectively implement the start-stop feature. During these stop-and-go situations, the repeated restarting of the engine may cause excess battery drain. Accordingly, an engine stop/start control system is desired that minimizes the power loss due to engine idling while also avoids overconsuming the battery.